Wilcon's pre-tax profit fell 3.3% to £23.7m for the six months to 30 June. The group said poor performances in Scotland and north-west England and increased overheads had hit margins, despite an increase in turnover. This rose 39% from £231m to £321m.
The group said it had started a recovery plan to improve returns by the end of the year and up to 250 jobs would go as costs were cut.
Leighton, the former Asda chief executive who took over at Wilcon in January 2000, said he had doubled the amount of time he is spending at Wilcon over the past two months.
He said: "I'm still the new boy on the block but I'm spending twice as much time at Wilcon than I'm contracted for. The results were very disappointing and unacceptable but we're taking action to address the problems and we'll be judged on our performance."
He conceded the jury was still out on him, chief executive John Tutt and Wilcon's other senior managers. However, he added that he expected the firm to meet the market's expectations by the end of the year.
Analysts were disappointed by the results, especially given the fact that rivals such as Wilson Bowden, Persimmon and Wimpey posted improving profits. They said Wilcon had lost control of its costs.
One analyst said: "It requires a special type of management technique to see margins fall 2.6%. They appear to have no problem selling houses but their costs are a real concern. They aren't telling a happy tale; if they can't make money in this climate then questions need to be asked."
Another said: "Despite all the plans they have tried, it doesn't get away from the fact that housebuilders rise or fall on the quality of their landbanks."
But Leighton said Wilcon's landbank was sound and pointed to the Wainhomes acquisition earlier this year as proof of that.
He said sales and selling prices were robust.
Leighton also blamed Wilcon's IT system for some of the problems.
He said a new system had not been well implemented and Wilcon had been forced to run another system at the same time, adding to its overheads.